Gas plasmas are widely used in a variety of integrated circuit (IC) fabrication processes, including plasma etching processes, plasma enhanced chemical vapor deposition (PECVD) processes, and physical vapor deposition (PVD) processes, such as plasma sputter deposition. Generally, plasmas for integrated circuit fabrication are produced within a processing chamber by introducing a process gas into the chamber at a sub-atmospheric pressure and then generating electrical and magnetic fields within the chamber. The electrical and magnetic fields generate an oscillating electron flow within the chamber. The oscillating electrons collide with and thereby ionize individual gas atoms and molecules by transferring kinetic energy through individual atomic collisions. The ions, radicals, neutrals, and free electrons collectively form what is referred to as a gas plasma or a glow discharge. The plasma may exist at various ionization levels from 10−6 up to fully ionized plasma (based on the fraction of ionized particles with respect to the total number of gas atoms or molecules).
There are various different methodologies for producing a plasma within a process chamber. For example, a pair of opposing charged electrodes might be oriented within the processing chamber to capacitively couple energy to the plasma. Alternatively, a microwave resonant chamber utilizing ultra-high frequency microwave fields might also be utilized. Electron cyclotron resonance (ECR) devices, on the other hand, use controlled magnetic fields in conjunction with microwave energy to induce circular electron flow within a process gas to create and sustain a plasma. Inductive coupling processes are also popular, and are particularly desirable for their capability of producing high-density plasmas within a processing chamber.
Inductively coupled plasmas (ICPs) are generally formed utilizing an electrically conductive element, often referred to as an antenna, which is positioned with respect to the processing chamber to inductively couple energy into the processing chamber and thus create and sustain a plasma therein. In one conventional inductively coupled plasma (ICP) system, an antenna in the shape of a coil is utilized and is biased with an RF power supply. Currents are developed in the coil which induce alternating or oscillating magnetic fields within the processing chamber. The oscillating magnetic fields within the chamber form and sustain the plasma. Various different antenna shapes and antenna orientations with respect to the processing chamber have been utilized for inductively coupled plasma systems. For example, a helical coil might be wound or wrapped around the outside of a cylindrical dielectric wall of the processing chamber to inductively couple energy into the chamber. Still further, a coil might be positioned within the processing chamber for creating and sustaining a plasma.
In one particular inductively coupled plasma (ICP) system, an inductive antenna is positioned proximate the top portion of the chamber to create a plasma within the chamber. More specifically, the antenna is positioned on one side of a dielectric plate or window at the top of the processing chamber, and energy radiated from the antenna is coupled through the dielectric window and into the plasma to form oscillating magnetic fields. Such a design is illustrated in U.S. Pat. No. 4,948,458, for example. A suitable dielectric material for a window or chamber sidewall of an ICP processing system is quartz. Various ICP systems are known and utilized in the art, as evidenced by various issued patents directed to such ICP systems. Such systems are designed for improving plasma processing parameters, such as plasma uniformity, RF matching, and the performance characteristics of the antennas or other inductive elements.
As noted above, in an ICP system, the plasma is excited by exciting electrons in the plasma region of the processing chamber using inductive currents which are derived from oscillating magnetic fields in the chamber. Those oscillating magnetic fields are produced proximate the inside of the dielectric window or chamber sidewall by RF currents within the antenna. The spatial distribution of the plasma-creating magnetic fields is a function of the sum of the individual magnetic fields produced by each portion or segment of the antenna, and those fields are affected, oftentimes adversely, by the other elements of the processing chamber and the geometry of the chamber. While current ICP systems and antenna designs utilized therein have provided sufficient plasma generation, such systems still have certain drawbacks.
For example, within an ICP system, the delivery of the oscillating magnetic fields or magnetic flux to the chamber is difficult to control. As a result, the field lines of the magnetic flux generated by the antenna extend outside of the processing chamber. The magnetic flux interacts with adjacent RF shielding and RF enclosures utilized in such systems to produce an opposed magnetic field that reduces or cancels a portion of the magnetic flux within the chamber. This effect is particularly significant if the RF shielding or enclosure is disposed near to the inductive antenna, such as due to space constraints in the ICP system.
Accordingly, it is an objective of the present invention to overcome drawbacks in the prior art and provide a plasma processing system, and particularly an ICP system, in which a dense, uniform plasma is created.
Among the objectives of the present invention is to control the distribution of the magnetic flux to provide for greater coupling efficiency of the magnetic flux from an inductive antenna into the processing chamber, to reduce the RF current and voltage in the inductive antenna for decreasing the incidence of arcing, and to eliminate the interaction of the antenna's magnetic flux with adjacent RF shielding and RF enclosures.
These and other objectives will become more readily apparent from the description of the invention set forth below.